Well if you're like me and keep up with both the manga as well as the anime, then you'll know how far apart they are.
If you don't keep up with both, here's a general description: The anime is nearing finish of the Sabody Archipelago Arc., and the manga is almost finished with the Impel Down Arc. (I believe)
Here is the spacing between the two
Sabody Archipeligo (10 mangas left) -> Amazon Lily (only 10 mangas) -> Impel Down (15 mangas so far)
So by adding this up, we know that the space between the two is only 35 mangas. The anime is at about manga 505, and the present manga is at 540.
Each anime incorporates at least 1-3 mangas into it, so we know what will inevitably happen.
My prediction is that the anime will go into GREAT detail of what became of the Straw Hat Pirates following being blasted off by Kuma. In the manga, it only really shows where the crew ended up. I expect about 25 filler episodes of this.
However, I'd like to hear all of your predictions. Go wild.